1. Field of the Invention
The present invention generally relates to an air conditioning system, such as for use in cooling and heating passenger compartments in automotive vehicles, and more particularly, to an air conditioning system having an improved structure for more efficiently cooling and heating automobile passenger compartments. Air conditioning system, as used herein, refers to a system that both heats and cools passenger compartment air.
2. Description of the Prior Art
Generally, closed automotive air conditioning systems experience a common problem in that during the cooling or heating operations, the air in the passenger compartment becomes either very dry or humid as the system cools or heats, respectively. Excessively dry air creates discomfort for the vehicle's passengers. The dryness occurs because the passenger compartment's air is continuously recirculated in a closed system, and the process of cooling recirculated air reduces its moisture content. Excessively moist air also creates discomfort for passengers, but more significantly, the moist air clouds up the passenger compartment's windows and thereby creates a safety hazard. Consequently, it is desirable to introduce fresh, outside air into the passenger compartment in order to better maintain the humidity level.
In prior art air conditioning systems, the introduction of outside air into the passenger compartment significantly decreases the efficiency of the heating and cooling process. For example FIG. 1 illustrates one type of conventional automotive air conditioning system that includes a refrigerating circuit comprising a first heat exchanger, a compressor, a second heat exchanger and a receiver-dryer, all of which are connected in series by a coolant pipe member. A thermal expansion valve is disposed between the receiver-dryer and the first heat exchanger. The system also includes a heater circuit comprising a heater core, a radiator and a blower. Such a system suffers from the above-described problem, namely, if fresh, outside air is introduced into the passenger compartment, the system's cooling and heating efficiency is significantly reduced.
Specifically, in a system such as that illustrated in FIG. 1, evaporator (i.e., first heat exchanger) 11 is disposed in passenger compartment 20 of an automobile, or more precisely, in duct assembly 30 which is located under dashboard 21 of the automobile. Duct assembly 30 includes duct 31 in which evaporator 11, heater core 32 and a blower (not shown) are disposed. Damper 33, which is also disposed in duct 31, selectively opens and closes outside air inlet opening 34 and passenger compartment air inlet opening 35 by pivotal movement thereof. Damper 33 is configured so as to pivot and close passenger compartment air inlet opening 35, and simultaneously open outside air inlet opening 34. In this configuration, the blower is used to introduce outside air into duct 31 through outside air inlet opening 34. In order to heat passenger compartment 20, heater core 32 acts as a heat source for the system by utilizing the heat generated from engine 50.
Condenser (i.e., second heat exchanger) 12 is disposed in engine compartment 60 and disposed at the front portion of the automobile or, more precisely, in front of radiator 51. Outside air is conducted into engine compartment 60, and is passed through condenser 12 and radiator 51, by the operation of condenser fan 13 and radiator fan 52. Accordingly, refrigerant in condenser 12 which is flowing from the system compressor (not shown) is heat exchanged with the outside air. That is, the refrigerant is condensed by radiating heat therefrom into the outside air.
In response to a demand to cool passenger compartment 20, outside air is continuously introduced into duct 31 through outside air inlet opening 34 and is passed through evaporator 11 by the operation of the blower. Consequently, outside air is heat exchanged with the refrigerant in evaporator 11. That is, the refrigerant in evaporator 11 is vaporized by absorbing heat from the outside air. Accordingly, the outside air is cooled and blown into passenger compartment 20, which is thereby cooled. The air in passenger compartment 20 is continuously vented to the outside of the automobile through ventilator 40 which is disposed at the two, rear quarter-panels of the automobile. Heater core 32 is not operated during the cooling operation.
In response to a demand to heat passenger compartment 20, outside air is introduced continuously into duct 31 through outside air inlet opening 34 and is passed through heater core 32 by the operation of the blower. Consequently, the outside air is heat exchanged with the fluid in heater core 32. Accordingly, the outside air is warmed and blown into passenger compartment 20, which is thereby heated. As in the cooling operation, the air in passenger compartment 20 is continuously vented to the outside of the automobile through ventilator 40. The air cooling part of the system is not operated during the heating operation.
In addition to the above-described, outside air inlet mode of operation, a system as illustrated in FIG. 1 utilizes two other air inlet modes of operation, such as the (1) passenger compartment air inlet mode and (2) mixed air inlet mode. In the passenger compartment air inlet mode, damper 33 is pivoted so that passenger compartment air inlet opening 35 is opened, and simultaneously, outside air inlet opening 34 is closed. In this configuration, the position of damper 33 is illustrated by the dashed line in FIG. 1. In the mixed air inlet mode, damper 33 is rotated to a central position so that both passenger compartment air inlet opening 35 and outside air inlet opening 34 are maintained in the open position.
A problem occurs while cooling in the passenger compartment air inlet mode of operation. The cooling process acts to remove moisture from the cooled air. Consequently, the humidity in passenger compartment 20 is significantly reduced, because only the compartment's air is circulated in this mode of operation. Such a lack of humidity produces discomfort for passengers in the automobile.
Another problem occurs while heating in the passenger compartment air inlet mode. Since only passenger, compartment air is circulated, the inside surfaces of the automobile windows fog or cloud up due to the high moisture content of the inside air relative to that of the outside air. This fogging or clouding of the windshield and the side and rear windows creates a safety hazard for passengers in the automobile. Therefore, it is desirable to use the outside air inlet mode as much as possible, in order to introduce a continuous flow of fresh, outside air into passenger compartment 20 and prevent the above-mentioned problems encountered in prior art systems.
Another problem is created by using the outside air inlet mode of operation while either cooling or heating the automobile passenger compartment. In the prior art, when the system is operated in the outside air inlet mode, passenger compartment air is mixed with a similar amount of outside air, and the mixture is then continuously vented from passenger compartment 20 to the outside of the automobile. However, since the outside air does not flow through, or utilize the cooling or heating contribution of, the second heat exchanger, the outside air's temperature is significantly different from that of the passenger compartment. Consequently, the overall cooling and heating efficiency of the system is lowered by a significant amount. As a result, operation of the air conditioner or heater in the outside air inlet mode, cannot be sustained for long periods of time if the outside air temperature is excessively hot or cold, respectively.
A heat pump may be used in an automobile air conditioning system to improve the cooling and heating efficiency of the system in the outside air inlet mode of operation. For example, Japanese Patent Application Publication No. 62-181909 discloses an automobile air conditioning system that includes a heat pump circuit. When the heat pump circuit is used for heating, the first heat exchanger is disposed in the passenger compartment and is used as a condenser. The second heat exchanger is disposed in the engine compartment and is used as an evaporator. However, in order to effectively maintain the heat exchanging capability of the second heat exchanger even if the outside air temperature is very low, this prior art provides a very complicated mechanism for conducting air to the second heat exchanger. This mechanism is made complicated because of the method used to provide hot air generated by the engine to the second heat exchanger.